Oxygen-carrying pigment in blood.

**The reasoning** Haemoglobin is the iron-containing protein found in red blood cells that binds to oxygen in your lungs and transports it throughout your body. Think of it as a delivery truck for oxygen. The "haemo-" part means blood, and the iron in haemoglobin is what makes blood red. When you breathe in, oxygen attaches to haemoglobin in your lungs, then your heart pumps this oxygen-rich blood to every cell in your body. This is basic human physiology — a core JAMB/WAEC Biology concept. **Why the wrong options tempt you** **Chlorophyll** tricks students who mix up Biology topics — it's the *green* pigment in *plants* that captures sunlight for photosynthesis, not oxygen transport in animals. **Melanin** is the pigment that gives your skin, hair, and eyes their color; it protects against UV rays but has nothing to do with oxygen. **Keratin** is a structural protein in your hair and nails — tough stuff, but it doesn't carry anything. **Quick takeaway** Remember: **Haemo = blood, globin = protein** — haemoglobin is literally "the blood protein" that carries oxygen from lungs to tissues.